Noisy Onan (gas 6.5 kw)

[DavidInWilmNC]

I finally got my generator enclosure mostly finished and insulated.  It's in the first bay behind the driver.  I lined the existing aluminum bay walls with 3/4" plywood and constructed the rest of the enclosure out of that as well.  I covered the inside of the entire area with high density 1/2" foam, and covered that with 'egg crate' foam.  I'm planning on using the same high density foam on the insides of the bay door where it's possible.  It's not too noisy iniside (got to get some better vibration isolators, though).  The exhause is a bit noisy.  I used a small automobile muffler, which is WAY too loud.  I'll probably add another inline to hush that.  The worst noise, though, is from the 'Vacu-flo' blower.  It blows directly out the bottom of the bus.  I was thinking that a small metal deflector, similar to what is used on home air supply registers, blowing back towards the rear of the bus might help.  I'm parked in the yard, on dirt, and I can only imagine how loud that will be with the noise reflecting off a hard surface.  I'm also thinking a bit of the 1/2" foam in the deflector and on the bottom of the bus might help with the reflected noise.  I know it wouldn't hold up well, but it's cheap and I've got lots of scraps to replace it with.  I know these old Onans are very common, but this is noiser than I've heard from most.  What have other done for this, or is this just the nature of this genset?  Thanks for any help or suggestions.

David

[TomC]

I had the 6.5 2 cylinder opposed on my truck that ran at 1800rpm.  The gen wasn't very noisy.  I did use a piece of cardboard to aim the warm air back under the truck that kept the engine and trans much warmer over night on sub freezing nights.  If you have a 3600rpm gen, I can understand the noise.  I would make a deflector that could be easily installed when stopped for the night, but just let run normally when driving. 
One thing that is missing that really quiets the gen is to use high density foam with a lead layer in the middle.  That REALLY works well.  Good Luck, TomC

[DavidInWilmNC]

Tom, that sounds like the model I have.  It's an old one with the points on the top and the main windings act as the starter.  It does run at 1800 rpm.  I used a scrap piece of aluminum to block the sound underneath as a test and it did make it somewhat quieter.  I like the idea of blowing the heat back towards the engine and trans.  I'd thought about adding a fitting to the blower housing to get some of that hot air into the bus on cold days & nights, but don't know about that idea.  It would also help keep the humidity down by introducing dry outside air to the bus.  This will probably just remain an idea, but it could be used to blow some warm air back to the tank bay in the winter.  Just a 2" defrost duct with a damper would be all that would be required.  What did you do for the muffler on yours?  I couldn't see spending the $75+ on the one from Onan when a couple of $17 automotive ones should work.  Thanks for the info.

David

[John Z]

I know the Onan mufflers on ebay are around 75.00. But i bought the correct one (and it works well) from the Onan dealer for about half that. Give them a call before spending more money trying to cobble up another cheap auto one.

[niles500]

"The worst noise, though, is from the 'Vacu-flo' blower.  It blows directly out the bottom of the bus"

HVAC duct board constructed w/ at least 2 - 90 degree elbows for both supply and discharge vents has worked well for others - HTH

[JackConrad]

David,
    We installed a baffle under the floor when we had our Onan. It not only helped with the noise level, but prevented stirring up all the dust, leaves, grass, etc.  We used a small car muffler and it reduced the noise to an acceptable level (I went to my favorite parts house and they said "go look through the mufflers and find what will work for you", I don't remember what car it was designed for). 
    I would be very hesitant about ducting any of this hot air into the bus interior. A slight exhaust leak could be deadly.  Jack

[DavidInWilmNC]

David,
    We installed a baffle under the floor when we had our Onan. It not only helped with the noise level, but prevented stirring up all the dust, leaves, grass, etc.  We used a small car muffler and it reduced the noise to an acceptable level (I went to my favorite parts house and they said "go look through the mufflers and find what will work for you", I don't remember what car it was designed for). 
    I would be very hesitant about ducting any of this hot air into the bus interior. A slight exhaust leak could be deadly.  Jack

Jack,
The parts place here also told me to go look through their mufflers.  It's a generic small one.  An additonal couple feet of length in the from the muffler seems to help some, too, so that's a possibility.  The only place that deals with Onan is naturally the Cummins dealer.  A friend bought a muffler for her little 2.5 Micro-somethng Onan and paid around $125 for it. 

About the baffle - I'm also thinking about the dirt blowing around.  I know the bus A/C condensor blower, while a lot stronger, stirs up quite a bit and the Onan does, too.  I won't use any of the hot air inside the bus; it was mostly just an idea... kind of like the old air cooled VW's. 

Thanks, guys.

David

[JackConrad]

David,
   I was told that running a larger diameter exhaust pipe (2") for a distance before the muffler would help absorb the pulsations and contribute to a quieter generator. We did this on our bus. Generator is in the old AC condenser compartment.  Exhaust goes through the floor, then a 2" exhaust pipe approx 15', a 90 degree sweep into a automotive type muffler and a chrome extension attached to the muffler to bring the exhaust out from under the bus (the muffler is crosswise in front of drive axle). This also put the exhaust noise at some distance from the generator. Wherever you stand, you are not near ALL the generator noises.  Jack

[DavidInWilmNC]

Jack,
That makes a lot of sense (the longer pipe thing).  I don't think I can go that far back, as I have the original MCI windows and that would put the exhaust right below them.  I'm sure I can add another 10 feet or so.  I agree, 'breaking up' the sound will make a big difference.  Thanks.

David

[JackConrad]

David,
    I made a vertical stack that we attach when camped to put the exhaust above the bus. Remember, hot air rises. When driving the air flow past the bus disperses the exhaust gas.  Jack

[DavidInWilmNC]

David,
    I made a vertical stack that we attach when camped to put the exhaust above the bus. Remember, hot air rises. When driving the air flow past the bus disperses the exhaust gas.  Jack

Jack, somehow, that doesn't surprise me.  I mean, you've got just about every other aspect of the whole bus conversion covered (and I say that sincerely)!  I'll probably pull the muffler, take it to my local 'son and pop' muffler shop that helped me before, and get them to flare the pipe to fit on the muffler and sell me some more pipe.  They were really cheap and helpful last time I went.  Since I need a tailpipe on my pickup, maybe they'll be glad to help me out again.  What did you use for the vertical stack?  I've seen them in RV catalogs, but they always seemed so damned expensive for what they were. 

David

[JackConrad]

     Let me try to explain my vertical stack. I started with a 90 degree sweep thatslips over the muffler extension. I installed a 24" section of exhaust pipe that points straight up when installed. I put a piece of 3" PVC pipe over the exhaust pipe and centered the exhaust pipe using 2 sets of 3 screws through the PVC pipe. One set near bottom of PVC pipe and one set near the top of the section of exhaust pipe. The screws are 120 degrees apart. I cut the PVC pipe into 2 6' lengths and connect them with a PVC connector (glue connector to top section only). This allows the pipe to be stored in the baggage compartment when traveling. I then added a small hook near the top that hangs on the drip rail.  As the hot exhaust gases go up the pipe they draw cool air in at the bottom (chimney effect). This helps keep the pipe cool as well as dilute the exhaust gaes.  Jack

[4104GA]

I used a chevy chevette diesel muffler on one of my onan generators and it really cut down the exhaust noise.  It is small and cheap.($22.00)
4104Ga.

[Ncbob]

Dave, the Vacu-flow can be rotated to a more favorable position if you so desire. It is not necessqary to remove the fan to do this.  Should be four bolts (behind the plugs) in the front of the duct.  I thought for sure I'd mentioned this to you in T'ville but I might be mistaken.

Good Luck.....

NCbob

[ChuckMC8]

bob, can the hot discharge air on my 7.5 Marquis be turned to discharge through the door rather than down thru the bus floor? The only complaint with it is that when the awining is extended and the geny running, the hot air comes up under the awning and is uncomfortable. The trick would be to make it where the discharge air would not be pulled back into the fresh air intake and recycled.
If it cant be turned, another suggestion to divert the hot air out?